Abstract
Wastewater treatment plants (WWTPs), linking human fecal residues and the environment, are considered as hotspots for the spread of antimicrobial resistance (AMR). In order to evaluate the role of WWTPs and underlying operational parameters for the removal of AMR, the presence and removal efficiency of a selected set of 6 antimicrobial resistance genes (ARGs) and 2 mobile genetic elements (MGEs) was evaluated by means of qPCR in influent and effluent samples from 62 Dutch WWTPs. The role of possible factors impacting the concentrations of ARGs and MGEs in the influent and their removal was identified through statistical analysis. ARGs and the class I integron-integrase gene (intI1) were, on average, removed to a similar extent (1.76 log reduction) or better (+0.30–1.90 logs) than the total bacteria (measured as 16S rRNA gene). In contrast, broad-host-range plasmids (IncP-1) had a significantly increased (p < 0.001) relative abundance after treatment. The presence of healthcare institutions in the area served did only slightly increase the concentrations of ARGs or MGEs in influent. From the extended panel of operational parameters, rainfall, increasing the hydraulic load of the plant, most significantly (p < 0.05) affected the treatment efficiency by decreasing it on average −0.38 logs per time the flow exceeded the average daily flow. Our results suggest that overall, WWTP treatments do not favor the proliferation of the assessed resistance genes but might increase the relative abundance of broad-host-range plasmids of the IncP-1 type.
Highlights
Antimicrobial resistance (AMR) is a growing problem worldwide
In Europe, wastewater is treated in wastewater treatment plants (WWTPs), and their effluents are commonly discharged into natural water bodies
We assessed the occurrence of different ARGs and mobile genetic elements (MGEs) in the influent of 62 WWTP
Summary
Antimicrobial resistance (AMR) is a growing problem worldwide. It is a natural and ancient phenomenon (D'Costa et al, 2011), its occurrence in natural environments has been accelerated by anthropogenic activities. One of the essential vectors for the dissemination of human-related AMRs into the environment is wastewater, as it collects fecal residues including antibioticresistant bacteria (ARB) and their genes (ARGs) (Baquero et al, 2008). The main goal of sewage treatment is to remove organic components (measured as chemical (COD) and biological (BOD) oxygen demand), phosphorus and nitrogen nutrients (P, N) as well as suspended solids, but not bacteria, or their genes (Council of the European Communities, 1991). The core biological secondary treatment units of WWTPs, involving activated sludge, are composed of open microbiomes comprising complex networks of microbial populations (Weissbrodt et al, 2014).
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